As is recognized by all, many applications exist which require the use of solutions from which solids and dissolved substances have been separated. Many processes have been developed heretofore for purposes of accomplishing this function of separation. One technique which has commonly been employed to remove solids from a solution is centrifugal separation. However, although centrifugal separation has proven to be highly effective for separating solids from a solution, it is not particularly a useful technique for the removal of dissolved substances from a solution and may even promote the retention of the dissolved substances therein. Another problem associated with the technique of centrifugal separation is that extremely high levels of centrifugal acceleration require high speeds of rotation to produce the desired separation within a reasonable period of time.
Another technique which is well known in the prior art which has been employed for purposes of purifying solutins is that of vacuum distillation. Vacuum distillation is often effective in removing solid substances from a solution because, as the solution is continuously evaporated, the dissolved substances accumulate and eventually precipitate from solution, thereby becoming just one more solid to be removed. One of the problems encountered with vacuum distillation, however, is that large concentrations of solids interfere with the surface evaporation rates thereby slowing down the process. Another difficulty has been adequately providing for the continuous removal of the solids remaining after the solution has been distilled. Another problem associated with the technique has been the difficulty of exposing sufficient surface area of the solution to the vacuum to achieve an acceptable rate of evaporation.
In an effort to obviate the difficulties described hereinabove which characterize the technique of centrifugal separation as well as that of vacuum distillation, a process and apparatus adapted to provide for the continuous mechanical purification of a solution containing solids and dissolved substances therein has been developed, and comprises the subject matter described and claimed in copending patent application, Ser. No. 303,425, filed on Nov. 3, 1972, which is entitled LIQUID PURIFICATION APPARATUS AND PROCESS, now U.S. Pat. No. 3,837,491 granted Sept. 24, 1974. The apparatus described therein is operable for separating the solids and the dissolved substances from the solution in a rapid and economical manner, and provides for the effective removal of the separated solids. This is accomplished by subjecting the solution simultaneously to both centrifugal separation and vacuum distillation.
The mode of operation of the apparatus of the aforereferenced copending patent application is such that the temperature of the solution therein will drop as the latent heat of vaporization drains heat from the solution as liquid is vacuum boiled off the solution. As a result heat must be added to the solution in order to replace that lost and maintain a constant or minimum temperature for the solution present in the apparatus. Since the liquid which is vaporized is subsequently condensed, and since the heat produced during condensation equals substantially heat loss occurring during vaporization, it is therefor desirable to provide a system in which the apparatus is associated with means operable for transferring the heat from condensation to replace the heat required for vaporization and to provide additional heat energy to compensate for other losses. The present invention is directed to a system embodying such means.
Accordingly, it is an object of the present invention to provide a novel and improved low temperature purification system which is operable to mechanically purify a solution in a continuous operation by separating therefrom the solids and dissolved substances contained therein.
It is also an object of the present invention to provide such a low temperature purification system which eliminates the need to provide an external heat source for supplying heat to offset the heat loss which occurs during vaporization.
It is another object of the present invention to provide such a low temperature purification system wherein a means is provided that is operable to replace the heat that is lost during the vaporization of the liquid of the solution to form liquid vapor, by transferring back to the solution the heat that is produced when this liquid vapor is condensed whereby to maintain the temperature of the solution substantially constant or above a preselected minimum.
It is still another object of the present invention to provide such a low temperature purification system wherein the heat transfer means is operatively connected in the system incuding the vaporizing means and the condensing means.
A further object of the present invention is to provide such a low temperature purification system wherein the condensing means is connected in the system between the means wherein the liquid of the solution is vaporized and the vacuum pump which is operable to pump the liquid vapor whereby to enable a smaller size vacuum pump to be utilized in the system since the major portion of the vacuum can be produced as a result of the condensation process.
Yet another object of the present invention is to provide such a low temperature purification system which is highly effective to purify solutions by removing therefrom solids and dissolved substances contained therein while yet embodying components which are relatively inexpensive to manufacture and relatively easy to employ.